🚀 go-pugleaf

In article <1993Jan3.220805.9323@smab.se>, hans@smab.se (Hans C Larsson)
wrote:
> 
> The problem arises when an unstable pulse train is *RECEIVED* by
> a D/A-converter *FROM* a digital transport.
> (I.e. between *TWO* boxes.)

I will take it that by 'between *TWO* boxes' you mean between the Theta
transport and an outboard DAC, or equivalently, those functional units of
any CD signal processing chain. Accordingly, I will use 'transport' to mean
the combination of mechanical elements, laser pickup, and support circuitry
that spin a disc and spit out a sequence of digital words representing the
digital signal, and DAC to mean that which takes the digital signal and
converts it to analog form.

> The receiver has to Phase Lock on a square wave which might not
> be very "square".

The 'receiver', which by your previous usage I will take to mean the DAC,
will get a consistently clocked signal from the transport. The transport,
with its own small buffer and feedback to the servo motor that spins the
disc, will have no trouble providing this regular signal. It in fact must,
if for no better reason than as a side effect of the necessary data
shuffling, error-detection and correction, and sub-code sifting that must
precede output to the DAC.

> From this you will get time-shift on the samples on the *RECEIVING*
> end since (virtually) all D/A-converters lacks any significant
> amount of buffer memory *COMBINED* with re-clocking of the signal.
> (The only exception that I know of is the (horrendously expensive)
> Technics SH-X1000 D/A converter).

I don't see any time shift creeping anywhere, certainly not related to the
mechanical characteristics of the transport when it is operating well
enough not to skip or otherwise catastrophically fail. The DAC should need
no buffer at all, since it is the responsibility of the transport to
provide regular data, and only the transport that has the necessary
connections to the disc servo motor to mechanically re-clock its output.
The transport must be successful at this task, or it will fail outright by
skipping or mistracking, not by allowing mechanical jitter to enter into
the timing of the data stream.

I would be interested in finding literature on this Technics DAC, which, if
it isn't just high-end BS, must be more than just a DAC. I can think of no
good reason for large buffers in a DAC except perhaps for digital signal
processing or skip protection. (The latter wouldn't function without some
sort of control signal from the DAC back to the transport.)

-Kerry